Side-by-side tax comparison between Idaho (5.3% top rate, flat) and Montana (5.65% top rate, graduated). See which state lets you keep more at every salary level, and how cost of living changes the picture.
Idaho uses a flat income tax (5.3% flat) while Montana has a graduated system (4.7-5.65%). On a $100K salary, Idaho takes $5,300 in state and local taxes compared to Montana’s $3,673 \u2014 a difference of $1,628.
Because Idaho has flat brackets while Montana is graduated, the gap between them changes at different income levels. Idaho’s flat rate is predictable, while Montana’s graduated brackets may benefit lower earners but penalize higher incomes.
Montana wins at 10 out of 10 salary levels tested. The advantage exists but is modest across the income spectrum.
| Salary | Idaho | Montana | Difference | Winner |
|---|---|---|---|---|
| $40K | $32,200 | $32,851 | +$651 | Montana |
| $50K | $39,705 | $40,519 | +$814 | Montana |
| $60K | $47,210 | $48,187 | +$977 | Montana |
| $75K | $57,563 | $58,783 | +$1,221 | Montana |
| $100K | $73,825 | $75,453 | +$1,628 | Montana |
| $120K | $86,835 | $88,788 | +$1,953 | Montana |
| $150K | $105,801 | $108,242 | +$2,441 | Montana |
| $200K | $138,287 | $141,542 | +$3,255 | Montana |
| $250K | $170,014 | $174,083 | +$4,069 | Montana |
| $300K | $199,429 | $204,311 | +$4,883 | Montana |
Take-home pay only tells part of the story. Idaho has a cost of living index of 95 while Montana is at 97 (national average = 100).
With similar costs of living (95 vs 97), the tax difference is the primary factor. What you see in raw take-home pay is essentially what you get in purchasing power: $77,711 in Idaho vs $77,786 in Montana.
For a single earner at $100K filing jointly, take-home becomes $79,410 in Idaho and $81,038 in Montana \u2014 a difference of $1,628. The gap remains similar regardless of filing status.
On paper, moving from Idaho to Montana would save $1,628/year on a $100K salary, or $8,138 over 5 years. But relocation involves real costs: moving expenses, potentially buying/selling a home, changing jobs, and adjusting to a new community.
At $1,628/year, the tax difference alone likely isn’t worth relocating for. Other factors — job market, lifestyle, family — should drive the decision. The tax savings are a nice bonus if you’re already considering the move for other reasons.